I did not find this griefed house on my own accord, I was called over to fix the grief by the owner. You say that the owner gave you permission to take it but unless you have proof that he/she said that, I cannot believe you. Anyone can say that someone allowed them to grief something. Also, the house/farm did not look cleanly torn down, random blocks were taken and it was left not removed, but torn apart. By modifying another players blocks, supposedly with permission, probably without permission, you were griefing and therefore I had to ban you. Unless you can get proof that you were allowed, your ban will stick.